diff --git a/app/src/main/java/io/heckel/ntfy/up/BroadcastReceiver.kt b/app/src/main/java/io/heckel/ntfy/up/BroadcastReceiver.kt
index 43cfe09..83b5387 100644
--- a/app/src/main/java/io/heckel/ntfy/up/BroadcastReceiver.kt
+++ b/app/src/main/java/io/heckel/ntfy/up/BroadcastReceiver.kt
@@ -11,7 +11,10 @@ import io.heckel.ntfy.util.randomString
 import io.heckel.ntfy.util.topicUrlUp
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
 import java.util.*
 import kotlin.random.Random
 
@@ -44,46 +47,51 @@ class BroadcastReceiver : android.content.BroadcastReceiver() {
             return
         }
         GlobalScope.launch(Dispatchers.IO) {
-            val existingSubscription = repository.getSubscriptionByConnectorToken(connectorToken)
-            if (existingSubscription != null) {
-                if (existingSubscription.upAppId == appId) {
-                    val endpoint = topicUrlUp(existingSubscription.baseUrl, existingSubscription.topic)
-                    Log.d(TAG, "Subscription with connectorToken $connectorToken exists. Sending endpoint $endpoint.")
-                    distributor.sendEndpoint(appId, connectorToken, endpoint)
-                } else {
-                    Log.d(TAG, "Subscription with connectorToken $connectorToken exists for a different app. Refusing registration.")
-                    distributor.sendRegistrationFailed(appId, connectorToken, "Connector token already exists")
+            // We're doing all of this inside a critical section, because of possible races.
+            // See https://github.com/binwiederhier/ntfy/issues/230 for details.
+
+            mutex.withLock {
+                val existingSubscription = repository.getSubscriptionByConnectorToken(connectorToken)
+                if (existingSubscription != null) {
+                    if (existingSubscription.upAppId == appId) {
+                        val endpoint = topicUrlUp(existingSubscription.baseUrl, existingSubscription.topic)
+                        Log.d(TAG, "Subscription with connectorToken $connectorToken exists. Sending endpoint $endpoint.")
+                        distributor.sendEndpoint(appId, connectorToken, endpoint)
+                    } else {
+                        Log.d(TAG, "Subscription with connectorToken $connectorToken exists for a different app. Refusing registration.")
+                        distributor.sendRegistrationFailed(appId, connectorToken, "Connector token already exists")
+                    }
+                    return@launch
                 }
-                return@launch
-            }
 
-            // Add subscription
-            val baseUrl = repository.getDefaultBaseUrl() ?: context.getString(R.string.app_base_url)
-            val topic = UP_PREFIX + randomString(TOPIC_RANDOM_ID_LENGTH)
-            val endpoint = topicUrlUp(baseUrl, topic)
-            val subscription = Subscription(
-                id = Random.nextLong(),
-                baseUrl = baseUrl,
-                topic = topic,
-                instant = true, // No Firebase, always instant!
-                mutedUntil = 0,
-                upAppId = appId,
-                upConnectorToken = connectorToken,
-                totalCount = 0,
-                newCount = 0,
-                lastActive = Date().time/1000
-            )
-            Log.d(TAG, "Adding subscription with for app $appId (connectorToken $connectorToken): $subscription")
-            try {
-                // Note, this may fail due to a SQL constraint exception, see https://github.com/binwiederhier/ntfy/issues/185
-                repository.addSubscription(subscription)
-                distributor.sendEndpoint(appId, connectorToken, endpoint)
+                // Add subscription
+                val baseUrl = repository.getDefaultBaseUrl() ?: context.getString(R.string.app_base_url)
+                val topic = UP_PREFIX + randomString(TOPIC_RANDOM_ID_LENGTH)
+                val endpoint = topicUrlUp(baseUrl, topic)
+                val subscription = Subscription(
+                    id = Random.nextLong(),
+                    baseUrl = baseUrl,
+                    topic = topic,
+                    instant = true, // No Firebase, always instant!
+                    mutedUntil = 0,
+                    upAppId = appId,
+                    upConnectorToken = connectorToken,
+                    totalCount = 0,
+                    newCount = 0,
+                    lastActive = Date().time/1000
+                )
+                Log.d(TAG, "Adding subscription with for app $appId (connectorToken $connectorToken): $subscription")
+                try {
+                    // Note, this may fail due to a SQL constraint exception, see https://github.com/binwiederhier/ntfy/issues/185
+                    repository.addSubscription(subscription)
+                    distributor.sendEndpoint(appId, connectorToken, endpoint)
 
-                // Refresh (and maybe start) foreground service
-                SubscriberServiceManager.refresh(app)
-            } catch (e: Exception) {
-                Log.w(TAG, "Failed to add subscription", e)
-                distributor.sendRegistrationFailed(appId, connectorToken, e.message)
+                    // Refresh (and maybe start) foreground service
+                    SubscriberServiceManager.refresh(app)
+                } catch (e: Exception) {
+                    Log.w(TAG, "Failed to add subscription", e)
+                    distributor.sendRegistrationFailed(appId, connectorToken, e.message)
+                }
             }
         }
     }
@@ -95,19 +103,24 @@ class BroadcastReceiver : android.content.BroadcastReceiver() {
         val distributor = Distributor(app)
         Log.d(TAG, "UNREGISTER received (connectorToken=$connectorToken)")
         GlobalScope.launch(Dispatchers.IO) {
-            val existingSubscription = repository.getSubscriptionByConnectorToken(connectorToken)
-            if (existingSubscription == null) {
-                Log.d(TAG, "Subscription with connectorToken $connectorToken does not exist. Ignoring.")
-                return@launch
+            // We're doing all of this inside a critical section, because of possible races.
+            // See https://github.com/binwiederhier/ntfy/issues/230 for details.
+
+            mutex.withLock {
+                val existingSubscription = repository.getSubscriptionByConnectorToken(connectorToken)
+                if (existingSubscription == null) {
+                    Log.d(TAG, "Subscription with connectorToken $connectorToken does not exist. Ignoring.")
+                    return@launch
+                }
+
+                // Remove subscription
+                Log.d(TAG, "Removing subscription ${existingSubscription.id} with connectorToken $connectorToken")
+                repository.removeSubscription(existingSubscription.id)
+                existingSubscription.upAppId?.let { appId -> distributor.sendUnregistered(appId, connectorToken) }
+
+                // Refresh (and maybe stop) foreground service
+                SubscriberServiceManager.refresh(context)
             }
-
-            // Remove subscription
-            Log.d(TAG, "Removing subscription ${existingSubscription.id} with connectorToken $connectorToken")
-            repository.removeSubscription(existingSubscription.id)
-            existingSubscription.upAppId?.let { appId -> distributor.sendUnregistered(appId, connectorToken) }
-
-            // Refresh (and maybe stop) foreground service
-            SubscriberServiceManager.refresh(context)
         }
     }
 
@@ -115,5 +128,7 @@ class BroadcastReceiver : android.content.BroadcastReceiver() {
         private const val TAG = "NtfyUpBroadcastRecv"
         private const val UP_PREFIX = "up"
         private const val TOPIC_RANDOM_ID_LENGTH = 12
+
+        val mutex = Mutex() // https://github.com/binwiederhier/ntfy/issues/230
     }
 }
diff --git a/fastlane/metadata/android/en-US/changelog/27.txt b/fastlane/metadata/android/en-US/changelog/27.txt
index cfcd689..9719556 100644
--- a/fastlane/metadata/android/en-US/changelog/27.txt
+++ b/fastlane/metadata/android/en-US/changelog/27.txt
@@ -6,6 +6,7 @@ Bugs:
 * Make messages with links selectable (#226, thanks to @StoyanDimitrov for reporting)
 * Restoring topics or settings from backup doesn't work (#223, thanks to @shadow00 for reporting)
 * Fix app icon on old Android versions (#120, thanks to @shadow00 for reporting)
+* Fix races in UnifiedPush registration (#230, thanks to @Jakob for reporting)
 
 **Thanks for testing:**